1. Technical Field
The present invention relates to a computer system and data sharing method.
2. Related Art
In recent years, there has been proposed iSCSI (Internet SCSI) capable of using an SCSI (Small Computer System Interface) command by using an IP (Internet Protocol) network. In the iSCSI technique, the SCSI command, data and the like are held in a TCP/IP (Transmission Control Protocol/Internet Protocol) packet and encapsulated. Thereby a storage device according to the iSCSI technique can be directly connected to the communication network and the computer connected to the communication network can read and write data by accessing the storage device (Patent Document 1: JP-A-2005-352844). In this related art, however, the case of using a common logical volume at the same time by a plurality of computers is not considered.
As another related art, which is not the technique related to iSCSI, the technique of using one storage device by a plurality of computers is known (Patent Document 2: JP-A-2005-346426).
When a plurality of computers use one shared storage device located at physically-distant places, an access response time becomes delayed. For example, the following times are to be generated: the communication delay time between each computer and the shared storage device; the waiting time for the completion of the previously-performed processing; the time required for mounting the shared storage device by the computer; and the time required for unmounting the shared storage device by the computer. Accordingly, the response time is to be delayed. In the related art, for this reason, different computers access the same shared storage device frequently and data cannot be shared, which is poor in usability.
In addition, when there are plural computers connected to the shared storage device, the request for command processing is to be concentrated on the computer with the greatest throughput. As a result, a huge backlog is generated to lower the usability.
Further, when the computer supporting iSCSI and the computer not supporting iSCSI exist in the same system, the computer without an iSCSI initiator cannot use the shared storage device based on iSCSI. Therefore, the request for command processing is to be concentrated on the specific computer with the iSCSI initiator and the load on the specific computer is to increase. As a result, a huge backlog is generated.
The invention has been achieved in view of the aforementioned problems, and an object of the invention is to provide a computer system and a data sharing method capable of preventing the increase of backlog and sharing data in the shared storage device by a plurality of computers by using iSCSI. Another object of the invention is to provide a computer system and a data sharing method capable of improving reliability and usability by allowing a direct access to the shared storage device only by the specific computers by using iSCSI. Further object of the invention will be clarified by the description of embodiment mentioned later.